True, I agree that it would have been suicidal, but this was the new improved "cocky" Earthforce.
I would have expected at least one attempt to call Delenn's bluff.

They were trying to put down rebellions everywhere at that moment--most of the colonies were revolting and declaring independence. This was actually a particularly vulnerable moment for the Earthgov/Clark regime, and they were going to try to retain as many of the colonies as they could--an effort that would be severely curtailed, at best, if they got into a war with the Minbari, so they cut their losses at Babylon 5. I think that turned out to be the only secession from Earth Alliance that succeeded, as they could now focus on militarily easier battles and keep most of the old EA together under their bootheel.

For all the bluster about "alien threats" in Earthgov propaganda, Earthgov's real plans seemed to center around consolidating what they had in a tighter and tighter fist (and of course using fear of such threats to help that along)--their program was internally rather than externally directed. They might have beat up on some minor alien powers here and there (we don't hear of anything for sure, at least IIRC, but we did see them intervene in an alien civil war in order to gain a strategic presence in that sector), but unlike the Centauri, they weren't going on risky offensives in every direction, nor did they want to, at that point anyway. If the Centauri Republic were Nazi Germany in terms of foreign policy, Earth was more Franco's Spain--or Stalin's USSR, between Molatov-Ribbentrop and Barbarossa, when they could consolidate internal control and control of their "sphere" (which did include smaller invasions of some minor powers, like the Baltics and Finland) while staying out of a larger war with major powers.

It's interesting that Earth and Centauri, the two emerging Shadow proxies in their latest war cycle, took these fairly different directions under their influence. I wonder what Clark answered when Morden first asked him "what do you want?" It may have been a very different, but equally acceptable, answer to the Shadows. Londo, in so many words, wanted to conquer alien worlds; Clark wanted to "conquer" his own people. I suppose these are two facets of "the dream" that the Shadows promote.